The invention relates to a flexographic printing ink, comprising a solvent, a colourant, a binder and additives, a flexographic printing ink concentrate, an improved flexographic printing method, and a substrate having a permanent print thereon.
Aqueous printing fluids for printing unsized webs, in particular cellulosic webs, by rotogravure, in particular by intaglio printing, employing water-soluble dyes and having good water insensitivity after drying of the fluid have been prepared by combining self-curing, water-soluble, cationic thermosetting resins and selected water-soluble dyes. The thermosetting resin cures or sets by drying of the printing fluid, and the cured resin entraps and/or reacts with the dye. The dye/resin combination must be selected with great care, since the dyes must be compatible with the resin in solution and must be capable of reacting with the cellulose, with the resin or, preferably, with both during the resin curing process.
Examples of such printing fluids are disclosed in U.S. Pat. Nos. 3,860,547, 3,864,296, 3,880,792, and 3,839,291. Suitable types of dyes are disclosed in U.S. Pat. No. 3,709,903.
Aqueous printing fluids comprising an aqueous solution of a dialdehyde, preferably glyoxal or glutaraldehyde and a water-soluble cationic dyestuff having a functional group capable of reacting with the aldehyde to produce a reaction product dyestuff having improved bleed fastness on cellulosic fibers are disclosed in U.S. Pat. Nos. 4,340,386 and 4,432,900. The pH of these printing fluids is preferably acidic with a pH from about 2 to about 7 being preferred.
According to U.S. Pat. Nos. 4,340,386 and 4,432,900 these printing fluids are suitable for conventional printing techniques such as rotogravure, intaglio or flexographic printing. The alleged advantage of the use of these printing fluids in comparison with a printing fluid not containing the dialdehyde is that the dialdehyde reacts with the dyestuff as a cross-linking agent producing a dyestuff reaction product, which is significantly more water insensitive than the unreacted dyestuff, especially on cellulosic fibers. These printing fluids can be printed directly onto an already formed cellulosic web and subsequently dried to form the reaction product dyestuff, which purportedly has excellent bleed fastness on the cellulosic fibers. A mordant or other means of affixing the dye to the cellulosic fiber is not required.
A flexographic ink formulation with a solvent consisting of about 20-50% water and about 40-70% of a co-solvent selected from the group consisting of polyhydroxy alcohols having at least one hydroxyl group per four carbon atoms, ethers of such alcohols and mixtures of such alcohols and ethers, a basic dye and a water-soluble polymeric acid is disclosed in EP Patent Application No. 179 319.
The polymeric acid is alleged to provide several functions:
It establishes the viscosity at a level which is high enough for flexographic or letter press printing. It secures a pH value of the ink which is sufficiently low, typically less than 7.0, to maintain the basic dye in solution and prevent the basic dye from going into the leuco form. Further it is mentioned that the polymeric acid forms a salt with the dye to render it insoluble in water but soluble in the solvent.
An aqueous flexographic ink formulation comprising (1) an aqueous medium having a dye, a pigment or a combination of a dye and a pigment dispersed therein and (2) a fixing amount of a water-soluble curable ammonium polyamidoamine and a method for printing or dyeing a substrate by applying this ink formulation to the substrate and subjecting the applied formulation to conditions sufficient to cure the ammonium polyamidoamine are disclosed in U.S. Pat. No. 4,402,748.
Allegedly, substrates printed with such inks do not exhibit the loss of print, bleeding, etc., observed for conventional ink formulations particularly when the printed substrate is washed in detergent, accordingly these ink formulations are claimed to be particularly useful in the printing of paper towels and other paper products as well as in the printing of woven and nonwoven fabrics.
Suitable dyes are water-soluble anionic dyestuffs which may react with the cationic radicals of the ammonium polyamidoamine so as to form heteropolar bonds. In addition to the colouring material and the fixing agent, these ink formulations may contain an organic solvent miscible with water, such as a glycol or a glycol ether, preferably ethylene glycol.
An aqueous flexographic ink formulation comprising a colouring material selected from an anionic dyestuff, a pigment or mixtures thereof and a cationic fixing agent based on a water soluble, high molecular weight, crosslinked polyether amine, and a method for printing tissue paper, wherein this ink formulation is used are disclosed in GB Patent Application No. 2,030,998.
Allegedly, these inks are particularly suitable for use in the flexographic process, in particular in printing cellulosic non-woven fabrics. Fixation of the printings occurs at room temperature after a period of about 72 hours, but the fixation process may be accelerated in known manner, e.g. by heat. Printings with improved fastnesses, e.g. to water, alcohol, etc., are said to be obtained on the non-woven fabrics, in particular when ink compositions containing a pigment are used. The fixation of the anionic dyestuff is allegedly due to a reaction between the dyestuff and the cationic radicals of the polyether amine on the non-woven fabrics so as to form heteropolar bonds.
A water-borne flexographic ink which is said to provide a water-resistant print is disclosed in GB Patent Application No. 2,087,418A. The colourant in this ink is the ammonium salt of Nigrosine Sulfonic Acid, which is used in a water-based acrylic flexographic ink. A typical formulation is: 2 g ammonium salt of Nigrosine Sulfonic Acid, 1 g ammonium hydroxide (conc.), 5 g distilled water and 25 g Joncryl 78 (an aqueous acrylic ester copolymer dispersion).
It is the object of the present invention to provide an improved flexographic printing ink comprising a solvent, a colourant, a binder and additives and an improved flexographic printing method, whereby compared with the prior art
working environment problems are substantially reduced or eliminated; PA1 the solvent, the colourant, the binder and the additives may be selected among environmentally acceptable substances; PA1 the printing apparatus may be cleaned by using environmentally acceptable cleaning liquids; PA1 an essentially aqueous solvent may be used without limiting the choice of colourants; PA1 the constraints on the selection of the combination of binder and colourant are substantially reduced; and PA1 high quality prints, in particular exhibiting satisfactory water insensitivity and excellent rub-off properties may be obtained by using water-soluble dyes as colourants. PA1 the solvent is essentially water; the colourant is a dye selected from the group consisting of basic dyes, acid dyes and disperse dyes, in the following referred to as "water-soluble dye", or a mixture of such dyes dissolved in the solvent; PA1 the binder is selected from aqueous (meth)acrylic resins dispersed in the solvent at a pH above 7, preferably at pH about 8-9; and PA1 the additives include a wax selected from the group consisting of polyolefin waxes, paraffin waxes and mixed polyolefin and paraffin waxes dispersed in the solvent. PA1 the water is present in an amount of at least 50% by weight, preferably at least 60% by weight, most preferred at least 75% by weight; PA1 the water-soluble dye/dyes is/are present in an amount of about 0.5-10% by weight, preferably about 1-6% by weight, more preferred about 1-5% by weight, most preferred about 2-4% by weight, calculated as solid material; PA1 the binder is present in an amount of about 4-20% by weight, preferably 7-17% by weight, most preferred 9-16% by weight, calculated as solid material; and PA1 the wax is present in an amount of 0.5-10% by weight, preferably 2-8% by weight, most preferred 3-7% by weight, calculated as solid material; PA1 defoaming agents, PA1 softening or coalescing agents, PA1 thickening or rheology modifying agents